1. Field of the Invention
This invention relates to coatable compositions useful in making abrasive articles. More specifically, this invention relates to abrasive articles made using coatable compositions which include free radically curable compositions, particularly those including colored abrasive particles and/or colorants.
2. Description of Related Art
Three common abrasive articles are coated abrasives, bonded abrasives, and nonwoven abrasives. A coated abrasive comprises a backing onto which abrasive particles are adhered with a binder, typically a thermoset binder cured in a large festoon oven. The backing may, for example, be selected from paper, cloth, film, vulcanized fiber, and the like, or a combination of one or more of these materials or treated versions thereof. The abrasive particles are typically chosen from flint, garnet, aluminum oxide, alumina zirconia, ceramic aluminum oxide, diamond, silicon carbide (either green or black), cubic boron nitride, and the like. In bonded abrasives, a slurry is prepared comprising a resin and abrasive particles. The slurry is placed in a mold, the resin is cured, typically using heat and pressure, holding the abrasive particles together to form a three-dimensional object. Examples of bonded abrasives include grinding wheels, honing sticks, dresser sticks and sharpening sticks. Nonwoven abrasives comprise an open, lofty, three dimensional web of fibers bound together at points where they contact by a binder, which may or may not include abrasive particles.
The above-mentioned abrasive articles may be produced using addition polymerizable compositions as binder precursors, wherein polymerization may be initiated in a variety of ways, including, for example, thermal decomposition of peroxides, radiation (particle or non-particle), or a combination of the two. The chain carrier in the propagation step may be either ionic or contain a free radical.
Addition polymerizable compositions, particularly free radically polymerizable compositions, are useful in producing abrasive articles. The free radically polymerizable compositions significantly reduce or completely eliminate the need for large festoon thermal curing ovens in the production of coated abrasives. However, the abrasive performance of these articles depends greatly on the curing conditions, such as the wavelength of non-particle radiation, the type and structure of the article being produced, the chemistry of the photoinitiation system used, the color of the abrasive particles, and the like.
For example, there is a wide variety of abrasive particle colors, such that those abrasive particles most suitable for radiation curing may not afford the most efficacious abrasive articles in terms of cut. On the other hand, those abrasive particles having a dark color (such as brown heat-treated aluminum oxide) may not allow radiation to be transmitted to produce the depth of cure necessary to yield efficacious abrasive articles.
Further, if the abrasive articles are produced using a web process, i.e., in large sheet-like structures (often referred to as "webs") which are wound onto a roll, the degree of cure also depends on the exposure time and depth of the coating to be cured.
There is thus a need in the abrasives art for coatable compositions (i.e., compositions having viscosity which allow coating via conventional means, such as knife coaters) which comprise abrasive particles (particularly colored abrasive particles), free radically polymerizable compositions, and photoinitiator systems, which produce efficient abrasive articles at high productions rates.
Caul et al., in U.S. Pat. No. 4,588,419, disclose coated abrasives made from a combination of acrylated epoxy resins and heat curable resins. The resins may include calcium carbonate filler and a suspending agent, the preferred suspending agent apparently being fumed silica. Pieper et al., U.S. Pat. No. 5,152,917, disclose the production of structured abrasives using techniques which are useful in the present invention. Pieper et al. and Caul et al., however, do not disclose use of the photoinitiator systems which are useful in the present invention, or how their use may afford a more efficient abrasive article or higher production rates.